HiMAP Team Publishes Post-Earthquake Assessment Report of Imja, Tsho Rolpa, and Thulagi Glacial Lakes in Nepal

On 25 April 2015, a magnitude 7.8 earthquake leveled parts of of several cities and villages, including Kathmandu. The result caused more than 8,000 deaths throughout the country, followed by a magnitude 7.3 aftershock on 12 May. Massive landslides wiped out entire villages, rivers were dammed by landslides, and the geologic and geomorphic integrity of high altitude mountains and glaciers was destabilized. Scientists began to worry that the seismic activity could also result in new GLOFs through the weakening of terminal moraines and destabilization of potential GLOF triggers, such as overhanging ice and landslides. The arrival of the monsoon rains could further destabilize mountainsides, hillslopes and moraines through the continuous soaking rains, melting of ice, and saturation of soils.  

Miraculously, none of Nepal’s 21 potentially dangerous glacial lakes burst out during the earthquake, possibly related to the fact that they were all frozen at the time. In order to fully understand what the impacts of the earthquake were on lake stability the High Mountains Adaptation Partnership (HiMAP) fielded a volunteer group of scientists, researchers, and citizens to conduct detailed remote sensing and field-based assessments of three of Nepal’s most dangerous glacial lakes—Imja (Everest region), Tsho Rolpa (Rowaling region), and Thulagi (Manaslu region) (see map, below).

The goal of the project was to conduct analyses of post-earthquake impacts on the structural integrity of the three glacial lakes that included detecting changes in water volume, discharge, end moraine stability, lateral moraine stability, seepage, glacial terminus, ice-cored moraines, and risk of flooding.  Information and data obtained about the lakes was to be shared with all partners at debriefings conducted at the end of each field expedition (roughly 20 days per assessment). In fact, each field study resulted in a set of overall summary conditions and recommendations meant for consideration by the Government of Nepal, donors, researchers, and local communities.

Above, location of Imja, Tsho Rolpa, and Thulagi glacial lakes.

Imja and Tsho Rolpa glacial lakes were chosen for detailed post-earthquake assessment because they were of immediate concern to the Nepal's Department of Hydrology and Meteorology (DHM), primarily because of their ranking as high risk lakes susceptible to flooding as a result of earthquakes, dam collapse, or other triggers. Further concern was expressed over the fact that all three contain either significant downstream populations and/or infrastructure (e.g., hydropower plants) that would be severely damaged and/or destroyed in the event of a GLOF. 

The HiMAP Team's report presents the results of three separate field expeditions to Imja, Tsho Rolpa, and Thulagi glacial lakes conducted between 3 June, 2015 and 3 August, 2015.  The report details, through photographs and descriptive text, the post-earthquake changes in villages, landscapes, and at each lake as measured and/or observed by the team. GLOF risk levels are suggested for each on the basis of field observations and measurements, remote sensing (satellite and repeat landscape photography), literature reviews and assessments, and flood and avalanche modeling.

Communities downstream of all three lakes are fearful of the likelihood of GLOFs occurring in the near future, and lack adequate information about existing or planned early warning systems (EWSs), lake risk reduction methods, and disaster management planning.

A summary of conditions found and list of recommendations designed to facilitate the reduction of risks posed by each lake. Detailed bibliographies are provided at the end of each chapter, as is a separate concluding section containing recommendations and next steps applicable to all three of the lakes.
   
The report concludes that Nepal has entered an era of accelerated catastrophic events (landslides, floods, avalanches, rockfall) related to climate change, and that increases in the number and frequency of GLOFs can be expected with confidence.

Recommended next steps to mitigate these new challenges include a detailed surveys of all 21 of Nepal’s dangerous lakes; the development of Nepal-specific risk reduction engineering methods; the strengthening of downstream community disaster management planning; and strengthening of the DHM’s glacial lake analysis and risk reduction capacities through creation of a Glaciological Unit.